Recurrent Aphthous Stomatitis (Canker Sores): This condition is characterized by the periodic appearance of painful, shallow ulcers in the mouth. It's a common condition in children and can be triggered by stress, minor mouth injury, or certain foods.

Herpes Simplex Virus (HSV) Infection: HSV can cause oral ulcers that recur over time. The primary infection often presents with more severe symptoms, but subsequent episodes can be milder.
Hand, Foot, and Mouth Disease: Although more common in younger children, this viral illness can cause mouth sores and can recur.
Allergic or Irritant Stomatitis: Allergic reactions to foods, medications, or oral care products, as well as irritants like sharp teeth or dental appliances, can cause recurring mouth sores.

Leukemia or Lymphoma: Although rare, these cancers can present with oral ulcers among other symptoms like fatigue, weight loss, and lymphadenopathy. Early diagnosis is crucial for effective treatment.
Autoimmune Disorders (e.g., Pemphigus, Lupus): Certain autoimmune conditions can cause recurring oral ulcers. These conditions require prompt diagnosis and treatment to prevent serious complications.
Infectious Mononucleosis (Mono): Caused by Epstein-Barr virus, mono can lead to oral ulcers, fever, and lymphadenopathy. While not usually deadly, it can lead to significant morbidity if not managed properly.

Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues, some types can lead to oral ulcers among other symptoms.
Behçet's Disease: A rare disorder that causes blood vessel inflammation throughout the body, leading to symptoms like recurring oral ulcers, genital ulcers, and eye inflammation.
Gastrointestinal Disorders (e.g., Crohn's Disease, Ulcerative Colitis): Some gastrointestinal conditions can have extraintestinal manifestations, including oral ulcers.